Transformer load indicator



July 5, 1949. D. M. DUINKER 2,475,017

TRANSFORMER LOAD INDICATOR Filed July 20, 1946 AGf/VT Patented July 5, 1949 TRANSFORMER LOAD INDICATOR Daniel Marie Duinker, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application July 20, 1946, Serial No. 685,206 In the Netherlands August 23, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires August 23, 1963 3 Claims. (Cl. 177-311) This invention relates to a circuit-arrangement for rectifiers which comprises a leakage transformer.

The invention purports to provide a rectifier of this kind with a current indicator.

The task of a current indicator is to give an indication of the current strength flowing at a given moment through the rectifier. With the aid of this indication it is possible to control whether the rectifier is in the normal operating position, or not. In the case of gas-filled rectifying tubes the position may, to a certain extent, be Judged by the light radiated by the discharge. This method is more or less faulty and, moreover, not always applicable, for example-not in the case of rectifiers comprising blocking-layer valves, since these do not exhibit any externally perceptible variations in the operating position.

The invention profits by the circumstance that in a leakage transformer the voltage of the secondary winding upon load strongly decreases, whereas the voltage of the primary winding in the different load positions remains substantially constant.

The circuit-arrangement according to the invention utilizes a current indicator, for example an incandescent lamp, which is fed by two voltages of opposite senses, of which one originates from a winding coupled to the primary circuit and the other from a winding coupled to the secondary circuit of the transformer, these windings being chosen such that the voltage of the former winding is approximately equal to the voltage of the latter winding at no-load. The operation of such a device is such that in the unloaded position the two voltages substantially compensate each other and the indicator does not give any indication, whereas in any other position, either in the normal operating position, or with shortcircuit, a definite indication occurs. It has been found that this method of current indication, which will be explained more fully by reference to the figure in the accompanying drawing, is highly reliable and, due to the possibility to utilize comparatively inexpensive parts, can be used with particular advantage in rectifying apparatus comprising blocking-layer valves, which nowadays are frequently used for the rectification of comparatively small powers (for example charging-rectiflers for accumulators) and which, as a matter of fact, cannot be provided with control devices whose cost is out of proportion to that of the total apparatus. Besides, it is also for small apparatus of importance that the parts for the current indication used according to the invention; 1. e. two transformer windings for which, if desired, use may .be made of portions of existing windings, and for example, an incandescent lamp, take up very little space.

If the indicating member used is an incandescent lamp, it is advisable to connect a resistance in series with it, since the resistance constituted by the filament has such a positive temperature coefficient that the percentage variation in the current flowing through the incandescent lamp is much smaller than the percentage variation of the voltage difference produced by the two said transformer windings. Owing to the series-connection with a suitably chosen resistance, it may be ensured that this disadvantageous influence of the temperature coeflicient is negligible, or a leastappreciably decreased.

For a good understanding of the character of the invention it is mentioned that in voltagestabilizing devices it is'already known to utilize a control member responding to the difference between a voltage which is constant or at least substantially constant at a varying load, and a voltage the value of which varies with the load. The invention, however, relates to a circuit comprising a simple indicating member (which consequently does not comprise a complicated regulating member) which also responds to a voltage difference similarly obtained, it is true, but which is used in particular in circuits comprising a leakage transformer.

In order that the invention may be clearly understood and readily carried into effect, it will be described more fully by reference to the accompanying drawing.

A primary winding 3 and a secondary winding 4,4 are arranged on a transformer core I on either side of a magnetic shunt 2 in a manner usual for a leakage transformer. The winding 4, 4' is connected to direct-current terminals 6 via blocking-layer valves 5. On the side of the magnetic shunt where the primary winding 3 is arranged, there is provided an auxiliary winding '1 connected in opposition to a portion 4, 8 of the secondary winding. An incandescent lamp of, for example, 6 volts 40 milliamperes is connected to the difference between the two voltages produced in these windings. A resistance In is included in series with the incandescent lamp.

The voltage of the winding I is given approximately the same value as the voltage produced by the portion 4, 8 of the secondary winding at no-load. Consequently, in the unloaded position of the rectifier the lamp 9 radiates no light or substantially no light. Upon load, however, the

voltage of the secondary winding 4, I and hence also the corresponding voltage of the winding 4. I decrease, whereas the voltage oi winding 1 remains substantially constant. Now, the voltage difference to which the lamp 8 is connected acquires such a value that it distinctly radiates light. The function or resistance It has already been explained hereinbeiore.

with a correct choice of the voltages oi the windings land 4, 8 and of theincandescent illament, it is possible to obtain a distinct light an ierence between a faulty'manlpulation (shorta circuit of the terminals 6, or wrong connection of the accumulator), at which the lamp I, lights up brightly, and the correct manipulation, at which the lamp radiates but a weak light.

It is evident that the auxiliary winding I may form a part of the primary winding 3, such as is the case at the secondary side with the windings l, 8 and l, 4 while, inversely, the two lastmentioned windings might alternatively be realized as separate windings. In addition, it is not necessary for the leakage transformer to be provided with a magnetic shunt. I

The described device has the advantages of being very simple, inexpensive and reliable and taking up little space.

What I claim is:

l. A load indicating circuit comprising an alternating current source, a leakage transformer having a primary winding connected to said source, an auxiliary winding coupled to said primary winding for developing allrst' indicating voltage, a secondary winding connected to the load and having a tap therein whereby a second indicating voltage whose amplitude at zero load is substantially equal to said first indicating voltage is developed between said tap and one end of said secondary winding, voltage responsive indicating means, and means to apply said first and second indicating voltages in phase opposition to said indicating means.

2. A load indicating circuit comprising an alternating current source, a leakage transformer having a primary winding connected to said source,an auxiliary winding coupled to said primary winding for developing a first indicating is substantially equal to voltage. a secondary winding connected to the load and having a tap therein whereby a second indicating voltage whose amplitude at zero load is substantially equal to said first indicating voltage is developed between said tap and one end or said secondary winding, an incandescent lamp, and means to apply said first and second indicating voltages in phase opposition to said lamp.

3. A load indicating circuit comprising an alternating current source, a leakage transiormer having a primary winding connected to said source, an auxiliary winding coupled to said primary winding for developing a first indicating voltage, a secondary winding connected to the load and having a tap therein whereby a second indicating voltage whose amplitude at zero load said first voltage is developed between said tap and one end of said secondary windin an incandescent lamp, and a resistance element connected in series with said lamp, said tap being connected to one end of said auxiliary winding, said one end oi said secondary winding being connected to the other end of said auxiliary winding through said seriesconnected lamp and element whereby said first and second indicating voltages are applied to said lamp in phase opposition, said element having a value at which the temperature coefficient of the resistance of said lamp is negligible.

DANIEL MARIE DUINKER.

REFERENCES CITED The following references are of record in the file of this patent:

UurrEnfsTATEs PATENTS Number Name Date 1,904,096 St. Clair Apr. 18, 1933 1,986,112 Logan Jan. 1, 1935 2,226,021 Schweitzer, Jr Dec. 24, 1940 2,243,162 Lee May 27, 1941 2,324,188 Beetem July 13, 1943 2,355,068 Graves Aug. 8, 1944 FOREIGN PATENTS Number Country Date 526,831 Great Britain Sept. 26, 1940 

